Erase ribbon feed

ABSTRACT

An erase ribbon feed mechanism incrementally feeds ribbon both before and after, but not during print impact to break an adhesive type erase ribbon loose from adjacent structures such as a card holder to which it may have become attached. The mechanism is thus made suitable for feeding an adhesive erase ribbon without creating shedding conditions that would make it unsuitable for feeding a cover-up type erase ribbon. Preferably, the card holder is made of polytetraflouroethylene and includes surface contact minimizing ridges adjacent the path of the erase ribbon. Where the ribbon lift action increases the span length of the erase ribbon, the feed occurring after impact is designed to take-up ribbon at a rate at least as great as the rate of decrease in ribbon span length to prevent accumulation of slack in the ribbon span.

United States Patent [1 1 Lehnhardt, Jr. et al.

[ 1 ERASE RIBBON FEED [75] Inventors: Robert W. Lehnhardt, Jr.; John O.

Schaefer, both of Lexington, Ky.

[73] Assignee: International Business Machines Corporation, Armonk, N.Y.

22 Filed: June 27,1972

21 Appl. No.: 266,764

[52] US. Cl. 197/181, 197/151 [51] Int. Cl B4lj 29/16 [58] Field of Search 197/82, 84, 151, 153, 157,

[56] References Cited UNITED STATES PATENTS 3,397,767 8/1968 Hobbs" 197/151 X 3,444,979 5/1969 Francisco .1 197/151 1,183,424 5/1916 Baldwin... 197/181 3,204,746 9/1965 Wolowitz. 197/151 X 3,154,185 10/1964 Kamp 197/156X 1,415,293 5/1922 Baldwin 197/181 3,643,779 2/1972 Anderson et a1... 197/151 2,425,967 8/1947 Toggenburger 197/151 2,609,077 9/1952 Schroder 197/151 r e1 85 15 $1 .68 7 n Bellini/Fl Jan. 29, 1974 2/1956 Page 197/151 10/1967 Goffet a1 197/151 X [5 7] ABSTRACT An erase ribbon feed mechanism incrementally feeds ribbon both before and after, but not during print impact to break an adhesive type erase ribbon loose from adjacent structures such as a card holder to which it may have become attached. The mechanism is thus made suitable for feeding an adhesive erase ribbon without creating shedding conditions that would make it unsuitable for feeding a cover-up type erase ribbon. Preferably, the card holder is made of polytetraflouroethylene and includes surface contact minimizing ridges adjacent the path of the erase ribbon. Where the ribbon lift action increases the span length of the erase ribbon, the feed occurring after impact is designed to take-up ribbon at a rate at least as great as the rate of decrease in ribbon span length to prevent accumulation of slack in the ribbon span.

6 Claims, 11 Drawing Figures PATENTED m 2 9 I974 SHEET 1 OF 3 ERASE RIBBON FEED C ROSS-REFERENCE TO RELATED APPLICATIONS Reference is made to co-pending US. Pat. No. 3,724,633 and to Application Ser. No. 102,696 LE9- 70-016), filed Dec. 30, 1970 and entitled, Automatic Erase Mechanism."

BACKGROUND OF THE INVENTION Typewriters having an erase ribbon mechanism employing either an adhesive, character lifting surface, or an over print, character cover-up surface have been proposed in various forms. The use of an adhesive material to lift an erroneous character from paper has the distinct advantage over a cover-up erasing material in that the color of the paper printed on is of no consequence. An adhesive ribbon, however, is more difficult to handle than a cover-up ribbon due to its tendency to become attached to adjacent structure. US. Pat. No. 3,724,633 discloses a feed system for an adhesive ribbon including a tension control system that positively retains tension in an adhesive ribbon to minimize or eliminate a loose ribbon span that could become attached to an adjacent structure of the typewriter.

While that improved tension control system successfully prevents firm attachment of adhesive ribbon to adjacent structure that could cause complete failure of the erase system or typewriter, we have found a tendency for adhesive ribbon to become lightly attached to structure such as the usual plastic card holder that is immediately adjacent the necessary path of the adhesive ribbon span. This light attachment can interfere with the proper lift of the adhesive ribbon span when erasing is desired. This interference could either be total in which case the adhesive ribbon would not be lifted at the printing point, or more likely it would be partial where the adhesive ribbon is either not lifted in time to receive the impact, or due to sticking followed by abrupt release, actually overshoots the print point and again is not positioned to receive the impact.

It is desirable that the mechanism for feeding an erase ribbon be capable of feeding a cover-up erase ribbon as well as an adhesive erase ribbon since each ribbon has its own advantages. The cover-up ribbon, for example, can operate to obliterate characters printed with inks that are not suitable for lifting by adhesive.

It has thus been an object of our invention to devise a ribbon handling system capable of reliably feeding and lifting an erasing ribbon in a typewriter whether the erasing ribbon be of the adhesive or cover-up type.

DISCLOSURE OF THE INVENTION Our invention involves the improved method of feeding an adhesive ribbon that is to be accurately lifted to an impact point. Essentially the method involves feeding the ribbon immediately before and after impact to insure by the feed motion that the ribbon is sheared free of any adhesion with adjacent structure that might otherwise interfere with the accurate lift of the ribbon. The total feed for each erase cycle is slightly larger than a character width to insure a completely fresh ribbon is available. We prefer to divide this total increment into a pre-print increment of one-third. the total feed and a post-print increment of two-thirds the total feed. Our method is implemented by the use of a ribbon feed cam having separate feed control surface portions that are respectively effective prior to and following impact. Since it is desirable to maximize the shear force before and after impact, our cam is designed to concentrate the feed motion into discreet increments and to provide a non feed operation during the time of impact. This non-feed operation at impact is also important in enabling reliable handling of a white cover-up form of erase ribbon which tends to flake or shed when impacted while feeding. Also there is noticed a tendency for the openings of characters such as a, p, and 0 to fill with white cover-up materialwhen impacted while the white ribbon is moving.

By the use of separate cam portions to control feed before and after impact, it is possible to independently design feed rates according to the particular requirements of the system before and after impact. This degree of versatility is particularly useful where the ribbon lift mechanism increases the length of the ribbon span at the active or lifted position over the span length at the rest position. Thus the feed or take-up following impact is preferably designed to be at least as great as the rate at which the ribbon span length decreases due to the restoration of the lift mechanism to the rest position. This design eliminates the possibility that slack might be generated to cause untracking of the ribbon. In our preferred configuration, the ribbon lift motion actually increases the ribbon span length by approximately two-thirds of a typical character width. The ribbon feed cam thus is designed to feed one-third of a character width of ribbon prior to impact and'twothirds of the character width following impact at the rate at which the ribbon is made available by the lift moving to its rest position.

The tendency of an adhesive ribbon to attach to the card holder or other adjacent structure 'is preferably minimized by the use of a suitable adhesive material such as polytetraflouroethylene and by the design of I contact area reducing protrusions in the surface of the card holder.

These and other objects, features, and advantages of our ribbon handling system will be apparent to those skilled in the art from reading and understanding the following more detailed description of a specific illustrative embodiment of the apparatus that implements our inventive method and wherein reference is made to the accompanying drawings, of which:

FIG. 1 is a fragmentary perspective view of a typewriter having an erase ribbon handling system constructed in accordance with our invention.

FIG. 2 is an enlarged fragmentary perspective view of numerous details of the ribbon handling system constructed in accordance with our invention.

FIG. 3 is a detailed vertical cross-sectional view of the erase ribbon take-up and feed mechanism taken along lines III-III of FIG. 2.

FIG. 4 is an enlarged broken away perspective view of a detail of construction of the ribbon lift mechanism shown in FIGS. 1 and 2.

FIG. 5 is a detailed top plan view of the erase ribbon supply mechanism wherein a supply ribbon support member is shown in phantom lines.

FIGS. 6 and 7 are perspective views respectively of ribbon supply rolls of an adhesive erase ribbon and a cover-up erase ribbon.

FIG. 8 is a detail perspective view of a supply spool support member employed in the erase ribbon handling system.

FIG. 9 is a fragmentary perspective view of ribbon lift, print, and feed cams that are configured to effect the improved ribbon feed method of our invention.

FIG. 10 is a side elevational view of a typewriter into which our ribbon method can be implemented, and

FIG. 1 l is a graphic representation of the ribbon lift, feed and print sequence employed in a preferred implementation of our invention.

Referring now more specifically to the drawings, in FIG. 1 there is shown a typewriter or character-bycharacter printer 10 which, for purposes of illustration is shown as being of the type described generally in U.S. Pat. No. 2,919,002. The typewriter 10 includes impacting means comprising a type element 16 that opposes a paper support platen 1 1 to form a print position or impact point 12 therebetween. A frame portion 13 of the typewriter 10 supports the platen 1 1 and also supports an escapement rack 14 and a rotatable print shaft 15 which together form a pair of track forming rails that extend along the length of the platen. 11. The type element 16 is mounted in a print element carrier 17 which in turn is slidably mounted on the rails 14 and 15 to enable movement of the print point 12 laterally along the platen 11. Normal typing is accomplished through the use of an ink ribbon 18 which for purposes of illustration can be packaged in a cartridge 19 and fed by an appropriate incrementing mechanism (not shown) all as completely disclosed in U.S. Pat. No. 3,604,549. The ribbon 18 is broken away in FIG. 1 so as to not cover other mechanism of a greater consequence to the present invention.

In accordance with our invention, an erase ribbon 20 attached at its opposite ends to a supply roll 21 and a disposable takeup spool 22 is assembled on the carrier 17 to expose an active span 23 adjacent the print point 12. The span 23 is tracked past typewriter structures such as a clear plastic card-holder 11a. To minimize sticking of an adhesive ribbon, at least the outer surface of card holder 1 1a is made of an abhesive material such as polytetraflouroethylene and is formed with contact area reducing protrusions 11b and lead in tapered regions 11c. The erase ribbon 20 is fed in character-size increments by a feed or advancing mechanism (see also FIGS. 2 and 3). The ribbon 20 is threaded at the right of the print point 12 past a non-lifting, barrel shaped guide member 50 to the disposable ribbon takeup spool 22 and to the left of the print point 12 through a ribbon lift guide 60.

The ribbon feed mechanism 30 drives the ribbon takeup spool 22 in a counterclockwise direction by engagement of a toothed drive wheel 31 with the periphery of the ribbon 20 wound on the spool 22. Drive wheel 31 is rotatably mounted on a pivoted platform 32 by shouldered screw 33. Spring 34 urges platform 32 counterclockwise about its pivot stud 35 so as to resiliently urge the drive wheel 31 into contact with the ribbon 20. A U-shaped drive wheel actuating arm 36 is pivotally mounted on the head of shoulder screw 33 and coaxially at another point not shown. The drive wheel 31 has a plurality of spaced windows 37 extending therethrough for receiving a bent tab pawl part 38 of the drive arm 36 which is urged downwardly by the resiliency of drive arm 36. A flexed washer 39 urges the drive wheel 31 upwardly against the head of the screw 33 and creates a frictional drag therebetween. The configuration of pawl 38 and the frictional drag provided by washer 39 creates a one-way drive that is effective upon oscillation of the drive arm 36 to incrementally rotate drive wheel 31 clockwise and takeup spool 22 counterclockwise to wind a character-sized increment of the ribbon 20 thereon.

Oscillation of drive arm 36is selectively produced by driving power taken from a ribbon feed cam 40 that is timed relative to the occurrence of print impact to being slidably keyed to the print shaft 15 which is rotated during each print cycle of the typewriter 10 (FIG. 1). Since it is desired to feed the erase ribbon 20 only during erase cycles and not with each print operation, a control mechanism 41 is provided to select operation of drive arm 36 only when an erase operation is desired. The control mechanism 41 includes a frame mounted selection or mode control bail 42 supported for pivotally positioning about its axis 42a by a keyboard control mechanism, as taught in above mentioned copending U.S. Pat. Application Ser. No. 102,696 to indicate whether anormal print or erase cycle is desired. Bail 42 is pivoted clockwise from its position as shown when an erase operation is desired. Pivoting of bail 42 displaces link 43 that is pivoted to the carrier 17 to move tail 44 from under cam follower arm 45. These events occur when cam 40 presents its high point to the follower 45. Follower 45 as thus conditioned is free to follow restore surface portion 40a (see FIG. 9) of cam 40 downwardly and pivot about its axis 46 under the influence of a spring 47 connected to the drive arm 36 which in turn is connected to the cam follower 45 through a tie rod 48 and bellcrank 49 that is pivoted to a mounting plate 17a on the carrier 17. Continued rotation of cam 40 positively drives follower 45 upwardly toward its original position, whereupon drive arm 36 is powered clockwise about the shoulder screw 33 and pawl 38 drives wheel 31 clockwise to rotate the takeup spool 22 counterclockwise thus feeding an increment of the ribbon 20. When normal printing is desired, link 43 is not pivoted by bail 42 and its end 44 prevents follower 45 from moving downwardly upon rotation of the cam 40, thus no ribbon 20 is fed.

Takeup spool 22 can be removed when full for replacement by counterclockwise pivoting a control handle 51 about the takeup spool axis 56 (FIG. 3). An over-center bow spring 53 is connected at its opposite ends to the control handle 51 through notch 54 and to a stud 55 on the carrier mounting plate 17a. Pivoting of control handle 51 brings projection 52 against the edge of platform 32 to drive platform 32 clockwise about its pivot stud 35 overcoming the force of spring 34 and moving the drive wheel 31 outwardly away from the periphery of ribbon 20 on the takeup spool 22. Takeup spool 22 now can be lifted vertically off its mounting stud 56 (see FIG. 3) for replacement. The counterclockwise pivotal movement of control handle 51 also moves the right hand guide member 50 forwardly from its position as shown to release tension in the ribbon 20 as this guide member 50 is mounted to the control handle 51 by a stud 57. When a new takeup spool 22 is placed on mounting stud S6 and ribbon 20 is threaded around guide member 50, the control handle 51 is pivoted clockwise to return the parts to the position shown in FIGS. 2 and 3. Note that in this position the platform 32 includes a flange part 58 that overlies a flange 22a of the spool 22 thus retaining the spool 22 on the stud 56. Also during the movement of control handle 51 to its position as shown in FIG. 2, the guide member 50 will be moved rearwardly against the ribbon to provide an initial tension in the ribbon span 23.

The control bail 42 also controls operation of the ribbon lift guide 60 by displacing a carrier mounted control link 61 counterclockwise about its pivot axis to move an intermediate member 62 forwardly against spring 62a to a position where a tab portion 62b thereof overlies a drive part 63 of a cam follower 64 that is pivotally mounted on the carrier 17. In this forward position, intermediate member 62 is driven upwardly by counterclockwise pivoting of follower 64 when driven by a ribbon lift cam 65 that is timed with the print cycle by being slidably keyed to the print shaft 15. The right end 62c of the intermediate member 62 engages a vertically reciprocable member 66 that is slidably mounted on a carrier portion 17b as best shown in FIG. 4. Member 66 is connected to the ribbon lift guide 60 by a pivot stud 67. The lift guide 60 includes a cam slot portion 68 that slidably receives a fixed stud 17c whereby upon vertical movement of the member 66, lift guide 60 is both lifted and pivoted clockwise about its pivot stud 67. This motion brings the erase ribbon span 23 into operative alignment with the print point 12 (see FIG. 1) to cause a character erasure upon impact of the type element 16.

To maintain as short a length as possible of the erase ribbon 20 between the supply roll 21 and the print point 12 and still accommodate the large motion required by the vertical reciprocation of the lift guide 60, the supply roll 21 is mounted on a platform 70 that is pivoted by stud 71 about an axis 72 to the mounting plate 17a. An arm 69 of the vertically reciprocable member 66 is connected by a pin 69a to a slotted arm 73 of the platform 70 whereby lifting of the guide 60 also pivots the platform 70 and the ribbon supply roll 21 carried thereby, counterclockwise to maintain a reasonably direct feed path for the ribbon 20 from the supply roll 21 to the lift guide 60.

Ribbon Tension Mechanism A mechanism 80 for maintaining reliable resilient tension on the span 23 of ribbon 20 is best shown in FIG. 5. The supply roll 21 includes either a core 24 (see FIG. 6) or a core (see FIG. 7) depending upon whether an adhesive erase ribbon or cover-up erase ribbon is employed. Both cores 24 and 25 include internal curved spline configurations 26 that are dimensioned to engage a vertically extending complementary curved spline shaped spindle 81 of a supply roll support member 82 (see especially FIG. 8). A stud 83 carried by platform 70 rotatably supports member 82 on the platform 70. The mutually complementarily configured splines 26 and spindle 81 provide a drive connection that tends to force the supply roll 21 downwardly by the application of ribbon tension thereby holding the ribbon supply roll 21 firmly in place against a bottom flange part 84 of thesupport member 82.

The mechanism 80 applies a resilient bias force 90 to the rotatable support member 82 to tension the ribbon 20. The force 90 has a tangential component in the direction opposite to the normal movement of the ribbon 20 during a feed operation as indicated by arrow 91. The tensioning mechanism 80 includes a multi-toothed ratchet-wheel-like cam surface 85 on support member 82 that is engaged by a pawl end 92 of an elongated, cantilever supported, stiff wire spring 93. The cam surface is made up of a plurality of inclined tooth-like contoured surface portions 86 that are successively engaged by the pawl end 92 as the ribbon 20 is fed by mechanism 30. When the erase mechanism stands idle, spring 93 exerts a rotational force 90 against a cam surface portion 86 tending to rotate the supply roll 21 in the direction opposite to the feed direction. Pawl part 38 (FIGS. 2 and 3) positively prevents unwinding of takeup spool 22 during idle conditions. Thus reverse rotation of supply roll 21 tensions the ribbon span 23. Any tendency for the ribbon 20 to stretch or for other parts of the mechanism to yield or vibrate may result in slight rotation of the supply roll 21 about its axis 87, however, pawl 92 will remain in positive contact with cam surface parts 86. Spring 93 thus remains effective to apply force 90 throughout a wide range of such movement. Note particularly that the resilient force by spring 93 is not capable of being lost or dissipated through slippage between the connection of pawl 92 and cam surface portions 86.

As explained above, a ribbon 20 having a contact adhesive surface 27 on a core 24 is shown in FIG. 6. This core 24 is characterized by having its internal splines 26 extend downwardly therefrom to provide a plurality of adjacent cylindrical segments or spline extension 28. These extensions 28 are employed to control the tension applied to the ribbon span 23. Wire spring 93 is wrapped at its right hand end (see FIGS. 2 and 5) about a post 94 that is carried by the platform 70. Also mounted on the post 94 is an intermediate bracket 95 that includes a tab 96 against which an end 97 of the spring wire 93 bears. A light tension spring 98 is anchored at one end to the tab 96 and at its opposite end to a tab 100 that is formed integrally with the platform 70. The bracket 95 also includes a control arm 101 that extends to a position under the bottom flange part 84 of the spindle 81 adjacent a stop part 99 formed integrally with the platform 70 and openings 88 that selectively receive the spline extensions 28.

When an adhesive ribbon mounted on a core 24 is employed, spline extensions 28 are received in openings 88 and project downwardly to a position adjacent the control arm 101 to trap the control arm 101 in its position as shown against the stop or tab 99. Bracket 95 thus is prevented from pivoting about its post 94, spring 98 is made ineffective, and spring wire 93 is flexed to accommodate the camming motion of cam teeth 86 past the pawl end 92 of the wire spring 93. I

On the other hand if a ribbon having a cover-up surface 29 and a core 25 is mounted on the spindle 81, there are no spline extensions 28 and thus the control arm 101 is not trapped against stop 99 and the bracket 95 is free to pivot about the post 94. Rotation of the spindle 81 causes pawl end 92 of the wire 93.to pivot counterclockwise about the post 94 as before, however due to the freedom of the bracket 95, this pivotal movement is accommodated by stretching of light spring 98 instead of flexing of the relatively stiff spring wire 93. It will thus be seen that the configuration of the ribbon supply core 24 or 25 is effective to select one of two tension levels by control of the freedom of bracket 95.

Ribbon Feed Sequence The method of our invention can be implemented in shown in FIG. 10 is initiated by depression of a keyboard key 110 to move a control interposer 111 to a position where it is trapped by a spring latch 112. Depression of interposer 111 depresses clutch control bail 113 to release a clutch latch 114 for movement by spring 115 to a position where cycle clutch 116 is permitted to rotate. Restore cam 117 rotates with cycle clutch 116 and returns clutch latch 114 to its latched position after 180 of clutch rotation. The rotation of clutch 116 drives a gear train 118 to rotate the print shaft 360.

Timed driving means such as print cam 120 is mounted on the print shaft 15 and acts on follower 121 to drive type element 16 about pivot axis 122 into impact with the platen 12 at the time of approximately 220 of rotation of the print shaft 15. The operation of print cam 120 is graphically shown in FlG. 11. The sequencing of our invention can best be understood with reference to the time of this impact occurrence.

As shown in FIG. 9 and also in FIG. 2, ribbon lift cam 65 and ribbon feed cam 40 are rotatably carried by print shaft 15 to rotate simultaneously with print cam 120. The ribbon lift cam 65 includes a rise surface portion 65a, a dwell surface portion 65b, and a fall or restore surface portion 65c. The profiles of these surface portions are shown graphically in FIG. 11. These surface portions control the rise and fall of guide 60 to position the span 23 of erase ribbon 20 either in an active position adjacent the impact point 12, or in a rest position as shown in FIG. 1 displaced below the impact point 12.

The ribbon feed cam 40 includes the restore surface portion 40a, an initial or pre-print feed rise portion 40b, a dwell or non-feed portion 40c, and a final or post-print feed rise portion 40a. The profiles of these surface portions are graphically shown in FIG. 11.

The particular operating sequence can now be generally understood with reference to FIG. 11 considering a print cycle initiated by depression of key 110 following erase selection by clockwise pivoting of bail 42 (FIG. 2). Depression of key 110 selects a single 360 rotation of print shaft 15 as described above. The initial rotation of print shaft 15 rest ores ribbon feed drive arm 36 by the ribbon feed cam restore surface 40a. Ribbon lift cam surface portion 65a begins to elevate: the ribbon span 23. At approximately 70 rotation of shaft 15, the pre-print feed surface 40b begins to drive the ribbon feed arm 36 to wind ribbon onto takeup spool 22 and continues this motion through l80 rotation of shaft 15. During this time, the ribbon lift cam surface portion 65a is also effective thus providing the maximum amount of input motion to the ribbon span 23 prior to print to break the ribbon loose from any adjacent structure such as cardholder 11a to which it may have become attached.

At approximately 180, both the ribbon feed cam 40 and the ribbon lift cam 65 present respective inactive surfaces 40c and 65b to their followers thereby causing the ribbon to become stationary for some period of time prior to the time of impact at approximately 220 as determined by-the print cam 120. The operation of surface portions 40c and 65b in holding the ribbon 23 still at the impact time of 220 is particularly important during feeding of an erase ribbon 20 having a white cover-up transfer layer 29 (FIG. 7) since lateral motion of the .character on the erase ribbon tends to cause shedding of the transfer layer and filling of open characters such as a, p, and o. The non-feeding action of the cam surface 400 is also important when feeding an adhesive erase ribbon since the feed is thereby concentrated into shorter, more abrupt increments to maximize the available force for shearing the ribbon loose from adjacent structure such as the cardholder 11a to which it may have becomeattached.

Following the occurrence of impact, ribbon lift cam 65 presents fall surface 650 to the follower 64 and the ribbon span 23 begins tomove downwardly to its rest position. At the same time, the ribbon feed cam 40 presents post-print feed surface 40d to its follower 45 to thereby drive arm 36 through a further feed increment to complete the ribbon feeding operation.

As stated above, the geometry of the ribbon span 23 (FIG. 2) as determined by guides 50 and 60 is such that the span 23 is two-thirds of a character width longer when guide 60 is lifted to its active position than when it is in its rest position. In the pre-print rotation of print shaft 15, when Cam surface portions 40b and 65a are effective, both the lift mechanism and the winding mechanism tend to unspool ribbon 20 from the supply spool 24 or 25. The additive unspooling effect is shown by curve in FIG. 11. Following print impact at 220 of the cycle, guide 60 is restored to its rest position and the length of the ribbon span path is shortened by the two-thirds of a character width it was initially lengthened.

To prevent accumulation of slack, the post-feed surface portion 40d of ribbon feedcam 40 is empirically profiled to wind ribbon 20 on takeup spool 22 at at least substantially the same rate as the ribbon span path is shortened. Curve 130 shows the cumulative effect of the lift and feed actions on ribbon unspooled from supply spool 24 or 25. Note that very little unspooling occurs following print impact. This result is achieved by configuring the ribbon feed cam surface 40d to just wind that ribbon made available to it by the fall motion of the lift guide 60 during effective operation of ribbon lift fall surface portion 65c.

While a specific preferred embodiment of our invention has been shown and described herein for purposes of illustration, it will be recognized by those skilled in the art that various modifications, additions, and substitutions can be made in applying the concepts disclosed to various workable systems. These concepts thus are to be limited only by the language of the appended claims:

We claim:

1. In a character-by-character printer having impacting means defining a print point and first timed driving means for establishing the time of impact occurrence, an erase ribbon handling mechanism separate from an inking ribbon mechanism and capable of lifting and feeding an adhesive erase ribbon, said erase ribbon handling mechanism including means supporting a spool of erase ribbon, guide means for receiving a span of said erase ribbon and including at least one lift member that is movably mounted for interposing said span at said print point of said impacting means, said printer having structure adjacent said span, and advancing means drivingly connected with said erase ribbon for advancing said erase ribbon along its length past said print point, the improvement comprising:

second timed driving means comprising cam means having a pre-print feed rise portion for positively driving said advancing means to advance a first increment of said erase ribbon past said print point prior to said impact time, said second timed driving means further controlling said advancing means to prevent advancement of said erase ribbon thereby during said impact, and said cam means having a post-print feed rise portion for positively driving said advancing means to advance a further increment of said erase ribbon subsequent to said impact time so that said cam rise portions provide a positive force to shear the ribbon from any structure to which it may become attached both before and after impact. 2. A printer as defined in claim 1 wherein the improvement further comprises:

third timed driving means operatively connected with said lift member for causing said lift member to displace said span from a rest position wherein said span is displaced from said print point to an active position wherein said span is superimposed upon said print point prior to said impact time and simultaneously with at least a portion of the time said advancing means is advancing said first increment of said erase ribbon, and further for moving said lift member to restore said span from said active position to said rest position subsequent to said impact time and simultaneously with at least a portion of the time said advancing means is advancing said further increment of said erase ribbon.

3. A printer as defined in claim 2 wherein said span of said erase ribbon has a length defined by said guide means that is substantially greater when said lift member is in its said active position than when said lift member is in its said rest position whereby the span length defined by said guide means decreases as said lift member is restored to its said rest position at a rate determined by said third timed driving means and wherein the improvement further comprises:

said post-print feed rise portion of said cam means having a rise sufficient to operate said advancing means to advance said further increment of said erase ribbon at a rate that is at least substantially as great as the rate of decrease in said span length occurring during restoration of said lift member to its said rest position. 4. A printer as defined in claim 1, wherein said erase ribbon comprises a contact adhesive surface.

5. A printer as defined in claim 4 wherein said structure located adjacent said span of erase ribbon has an external surface comprised of polytetraflouroethylene.

6. A printer as defined in claim 5 wherein said structure located adjacent said span comprises an external surface including protrusions for reducing the potential contact area between said erase ribbon and said struc- 

1. In a character-by-character printer having impacting means defining a print point and first timed driving means for establishing the time of impact occurrence, an erase ribbon handling mechanism separate from an inking ribbon mechanism and capable of lifting and feeding an adhesive erase ribbon, said erase ribbon handling mechanism including means supporting a spool of erase ribbon, guide means for receiving a span of said erase ribbon and including at least one lift member that is movably mounted for interposing said span at said print point of said impacting means, said printer having structure adjacent said span, and advancing means drivingly connected with said erase ribbon for advancing said erase ribbon along its length past said print point, the improvement comprising: second timed driving means comprising cam means having a preprint feed rise portion for positively driving said advancing means to advance a first increment of said erase ribbon past said print point prior to said impact time, said second timed driving means further controlling said advancing means to prevent advancement of said erase ribbon thereby during said impact, and said cam means having a post-print feed rise portion for positively driving said advancing means to advance a further increment of said erase ribbon subsequent to said impact time so that said cam rise portions provide a positive force to shear the ribbon from any structure to which it may become attached both before and after impact.
 2. A printer as defined in claim 1 wherein the improvement further comprises: third timed driving means operatively connected with said lift member for causing said lift member to displace said span from a rest position wherein said span is displaced from said print point to an active position wherein said span is superimposed upon said print point prior to said impact time and simultaneously with at least a portion of the time said advancing means is advancing said first increment of said erase ribbon, and further for moving said lift member to restore said span from said active position to said rest position subsequent to said impact time and simultaneously with at least a portion of the time said advancing means is advancing said further increment of said erase ribbon.
 3. A printer as defined in claim 2 wherein said span of said erase ribbon has a length defined by said guide means that is substantially greater when said lift member is in its said active position than when said lift member is in its said rest position whereby the span length defined by said guide means decreases as said lift member is restored to its said rest position at a rate determined by said third timed driving means and wherein the improvement further comprises: said post-print feed rise portion of said cam means having a rise sufficient to operate said advancing means to advance said further increment of said erase ribbon at a rate that is at least substantially as great as the rate of decrease in said span length occurring during restoration of said lift member to its said rest position.
 4. A printer as defined in claim 1, wherein said erase ribbon comprises a contact adhesive surface.
 5. A printer as defined in claim 4 wherein said structure located adjacent said span of erase ribbon has an external surface comprised of polytetraflouroethylene.
 6. A printer as defined in claim 5 wherein said structure located adjacent said span comprises an external surface including protrusions for reducing the potential contact area between said erase ribbon and said structure. 